In hip replacement procedures, a cavity must be formed in the medullary channel to receive a femoral implant stem. Implant stems generally have an egg-shaped cross section similar to the cross section of the femur. The receiving cavity must conform to the geometry of the implant stem. Milling the bone stock to form the cavity is preferable to reduce the trauma to the bone tissue.
A variety of broaches, rasps and milling instruments have been developed to prepare a cavity for receiving an irregularly shaped implant stem. Milling devices such as the ones described in U.S. Pat. No. 5,047,033 are used to cut and shape the cavities for custom fitted implants. The milling device includes a V-shaped guide frame having a lower end base portion that is adapted to extending into the medullary channel, and a pair of spaced struts. The lower end has one or more receptacles for holding the end of the mill or rotary reamer. This apparatus can be used to produce an irregular cavity but the anterior and posterior volumes of an egg-shaped cavity are not created simultaneously.